These days, image sensors in solid-state image sensing apparatuses such as a digital still camera have abruptly increased the number of pixels, and need to perform high-precision image processing at high speeds.
To achieve high-precision automatic focus adjustment (to be referred to as AF hereinafter) at high speeds, there has conventionally been proposed a technique of arranging AF pixels (to be referred to as focus detection pixels hereinafter) as some pixels of an image sensor 601, as shown in FIGS. 7 and 8. As shown in FIG. 7, the light receiving portion is divided to make pupil positions symmetrical to each other. One light receiving portion is defined as a focus detection pixel (A image) 501, and the other is defined as a focus detection pixel (B image) 502.
As shown in FIG. 8, the focus detection pixels (A images) 501 and focus detection pixels (B images) 502 are scattered at a certain ratio to all the pixels of the image sensor. Focus detection is done by comparing the phase differences between focus detection pixels (A images) 604 and focus detection pixels (B images) 605 at the same horizontal position.
In the conventional arrangement, focus detection pixels are arranged discretely, so an alias (aliasing) readily occurs and greatly degrades the AF performance.
As a conventional technique for reducing aliases contained in pixel information, the following proposals have been made.
Japanese Patent Laid-Open No. 9-65219 proposes a technique of repeating the displacement of an image sensor by a shift means to form an equivalently optical low-pass filter, thereby effectively avoiding generation of aliasing of a video signal.
Japanese Patent Laid-Open No. 9-74524 proposes the following technique. When moire is detected upon receiving an image of the first resolution, an image of the second resolution increased by an image shift means is generated. If no moire is detected, no moire removal circuit operates, suppressing power consumption.
However, the proposals by Japanese Patent Laid-Open Nos. 9-65219 and 9-74524 are not aimed at reducing aliases of focus detection pixels scattering in an image sensor. These references do not mention a measure against camera shake. In general, detection of a positional shift amount by matching calculation using an alias-containing image tends to fail. Thus, conventional techniques hardly reduce aliases of focus detection pixels.